The red oak borer, Enaphalodes rufulus (Haldeman)3, is an
important member of the oak borer complex that permanently damages the wood of
living oak trees and causes a decrease in lumber grade. The loss in grade can
amount to 40 percent of the current tree value, which, at today's prices, is
about $80 per thousand board feet for factory grade lumber in terms of reduced
quality caused by larval tunnels. About 38 percent of the oak wood used for
lumber, cooperage, and veneer in the Eastern United States is affected.

The red oak borer is native to North America, where it occurs naturally from
southeastern Canada and Maine to Florida, and west to Minnesota, Iowa, Oklahoma,
and Texas. The distribution map (fig. 1) presents all known county collection
records, with the exception of Brewster and Jeff Davis Counties in Texas. This
borer also has been found in ornamental nursery stock and shade trees outside
its natural range.

Figure 1.-Range of the red oak borer in the United States.

The red oak borer has been found in many oak species. Economic loss occurs
when borer tunnels and subsequent wood overgrowths in attacked trees are
distributed on the grading surfaces of boards and veneer. Wood-inhabiting
insects such as carpenterworms, timberworms, and carpenter ants use red oak
borer tunnels to gain entry into oaks. These other pests extend and increase the
damage begun by the red oak borer. Decay organisms also gain entry into oak
heartwood through borer tunnels.

The fine larval frass (fig. 2) is found during the first fall and winter after
eggs hatch. Wet spots (fig. 3) and medium-sized larval frass can be found during
the first spring and early summer. Discolored bark patches (fig. 4) and large
quantities of larval frass occur in the second fall and winter (fig. 7). Wood
slivers are extruded in the spring and early summer just before the adult
emerges (fig. 5). The adult exits through an oval hole which it chews in the
bark (fig. 6).

Figure 5. -Slivers are the remains
of a "plug" constructed by the overwintering larva and pushed
out of the tunnel during the
second spring activity period.

Figure 6. -An oval exit hole is made through the bark
near the initial attack site.

Figure 7. -Frass accumulates base of an attacked tree.

Life Stages

The red oak borer has a 2-year synchronous life cycle. The pest has been
studied in Pennsylvania, West Virginia, Ohio, Kentucky, Indiana, Illinois, and
Missouri (fig. 8). In nearly all cases adults emerged in odd-numbered years.

Figure 8. -Life history of the red oak borer in the North Central
United States

The adults (fig. 9) are nocturnal and can be found from mid-June to
mid-August. The sex ratio in natural populations is nearly 1 to 1. Mating takes
place on the host tree and the female lays an average of 110 eggs. The eggs are
attached with an adhesive in cracks, and under lichen patches and vines on host
trees. Often, as many as 95 percent of the eggs hatch.

The young larvae begin boring directly through the bark and spend their first
year in the phloem and sapwood making small (2 by 3 by ½ in.) (5 by 7.5 by
1.2 cm.) tunnels (fig. 10). The 2-year-old larvae make larger mines (7 by 3 by ½
in.) (15.5 by 7.5 by 1.2 cm.), and tunnel into the heartwood to construct a
pupal cell (fig. 11). The adult emerges near the original oviposition site by
gnawing an oval hole through the bark.

Woodpeckers are the most important recognized natural control agents of
the red oak borer, often reducing larval numbers by 40 percent. Winter feeding
activity by the hairy woodpecker, Dendrocopus villosus, and the downy
woodpecker, D. pubescens, is most successful against first year larvae
because these larvae overwinter in shallow furrows in the inner bark. The success
of woodpecker at the predation on second year larvae (fig. 12) within the wood
depends on the placement of the woodpecker work relative to the site where the
borer entered the wood. Excavation by woodpeckers at the entrance site can reduce
adult red oak borer emergence by only 16 percent, but excavation away from the
entrance site can result in 40- to 86-percent reduction.

Predation by the formicid ants, Aphaenogaster flemingi M.R. Smith and
A. treatae Forel, also provides some degree of natural control.

Applied Control

Borer impact studies showed that only about half of the borer-caused defects
produce lumber or veneer degrade. The remaining defects produce no degrade
because of their size, location, or association with other degrade-producing
factors such as rot, knots, and wane. When the grader disregarded half the red
oak borer-caused defects, lumber grade improved and borer impact was almost
eliminated. Therefore, any control practice which reduces borer damage by 50
percent will eliminate most borer-caused degrade.

Silvicultural control of the red oak borer has been achieved by removing
infested trees from timber stands. Population reductions of 95 percent have been
achieved over a 5-year period by this approach. Cultural controls are aimed at
decreasing borer numbers in pole-size stands of red, black, scarlet, and white
oaks, which reduces the chances of subsequent borer attack in the residual stand
throughout its rotation.

References

Berry, F.H. 1978. Decay associated with wounds in living oaks. U.S.
Department of Agriculture Forest Service Research Note NE-268, 2 p.